I. Field of the Invention
The invention is related to control systems for heat engines and, in particular, to a pro-active control system in which fuel flow rate and air flow rate are changed simultaneously.
II. Description of the Prior Art
Various methods for controlling the operation of internal combustion or heat engines are known in the art. Today, in most of the fuel control systems for internal combustion engines, the quantity of fuel or fuel flow rate being supplied to the engines is determined from the quantity of air being supplied. Some of the control systems use air flow sensors which directly measure the quantity of air being supplied to the engine such as the engine control systems taught by Oyama et al in U.S. Pat. No. 4,205,377 and 4,825,838, Koji et al in U.S. Pat. No. 4,517,946, and van Bruck in U.S. Pat. No. 4,677,559. These fuel control systems also use an oxygen sensor to maintain a predetermined partial pressure of oxygen in the engine's exhaust; preferably, on the lean side of stoicheometric.
In other engine control systems, the air flow to the engine is computed as a function of engine speed and the pressure of the air in the engine's intake manifold or the position of the throttle plate in the intake manifold.
Other engine control systems known in the art use alternate engine parameters for closing the loop from the engine back to the electronic controller. L. Taplin in U.S. Pat. No. 3,789,816 teaches a lean burn fuel control system in which the air flow rate is held constant and the fuel flow rate is decremented until the engine vibrates at a predetermined amplitude referred to as engine roughness. The fuel flow rate is then dithered to maintain a predetermined engine roughness. The engine roughness in the engine control system taught by Taplin is measured by a vibration sensor attached to the engine.
C.K. Leung, in U.S. Pat. No. 4,344,140, teaches an improvement to Taplin's engine control system in which engine roughness is determined by measuring the instantaneous rotational velocity of the engine's flywheel. In the fuel control system taught by C.K. Leung, the roughness signal is used to bias the fuel rate being supplied to the engine to maintain the engine roughness at a predetermined level.
In a similar manner, Latsch in U.S. Pat. No. 1,616,162, Binachi et al in U.S. Pat. No. 4,172,433, and Frobenuis in U.S. Pat. No. 4,140,083, all disclose engine control systems in which the fuel delivered to the engine is controlled or adjusted to maintain the fluctuations of the rotational speed of the engine's output at a predetermined value.
In an alterative engine control system, Latsch in U.S. Pat. No. 4,064,846, teaches an engine control system in which an engine control variable, such as fuel, air, or ignition timing, is modulated and the phase of the resultant variations in crankshaft's acceleration is used to adjust the magnitude of engine control variable.
These engine control systems collectively are reactive control systems in which the fuel flow rate is controlled in response to a change in the air flow rate to the engine, i.e., the opening of the throttle valve in the air intake manifold. In contrast, the engine control system described herein is a pro-active engine control system in which the fuel flow rate and the air-flow rate are changed, simultaneously, to maintain the ratio of air to fuel being supplied to the engine at a predetermined or desired air-fuel ratio.